Half-precision extension

The Half-precision extension is an optional architecture that
extends both the VFPv3 and the NEON architectures. It provides VFP
and NEON instructions that perform conversion between single-precision
(32-bit) and half-precision (16-bit) floating-point numbers.

The half-precision instructions are only available on NEON
or VFP systems that implement the half-precision extension. The
VFP variants that implement the half-precision extension are VFPv3-FP16,
VFPv3-D16-FP16, and VFPv4.